Submerged hose arm stabilizing means for single point mooring systems

ABSTRACT

In a single anchor leg mooring system, the submerged hose arm pivotally connected to the upstanding fluid cargo pipe is provided with a buoyancy tank and ballast weight located substantially outwardly from the pipe and beneath the center line of the buoyancy tank. As the pipe oscillates due to wind and wave action on the mooring buoy, the tendency of the hose arm to rock correspondingly is counteracted by the tendency of the ballast weight to remain in or return to its stable position vertically beneath the supporting buoyancy tank. This stabilizing means prevents excessive strains on the attached hose as the arm may otherwise droop too far down or rise too far above the optimum position.

Pedersen May 20, 1975 SUBMERGED HOSE ARM STABILIZING MEANS F OR SINGLEPOINT MOORING SYSTEMS [75] Inventor: Kristen l. Pedersen, Scarsdale, NY.

[73] Assignee: Sofec, lnc., Houston, Tex.

[22] Filed: Dec. 17, 1973 [21] Appl. No.: 424,958

[52] US. Cl. 9/8 P [51] Int. Cl B63b 21/52 [58] Field of Search 9/8 P, 8R;114/121, 123, 114/124, 126

[56] References Cited UNITED STATES PATENTS 3,641,602 2/1972 Flory etal. 9/8 P 3,651,525 3/1972 Rutten et al 9/8 P Assistant Examiner-StuartM. Goldstein Attorney, Agent, or FirmBertram H. Mann; Frank B.

Pugsley Primary ExaminerDuane A. Reger [57] ABSTRACT In a single anchorleg mooring system, the submerged hose arm pivotally connected to theupstanding fluid cargo pipe is provided with a buoyancy tank and ballastweight located substantially outwardly from the pipe and beneath thecenter line of the buoyancy tank. As the pipe oscillates due to wind andwave action on the mooring buoy, the tendency of the hose arm to rockcorrespondingly is counteracted by the tendency of the ballast weight toremain in or return to its stable position vertically beneath thesupporting buoyancy tank. This stabilizing means prevents excessivestrains on the attached hose as the arm may otherwise droop too far downor rise too far above the optimum position.

2 Claims, 6 Drawing Figures SUBMERGED HOSE ARM STABILIZING MEANS FORSINGLE POINT MOORING SYSTEMS BACKGROUND OF THE INVENTION This inventionrelates to so-called single point or single anchor leg mooring systemsand consists particularly in novel means for stabilizing the hose armpivotally connected to the upstanding cargo pipe and projectinglaterally therefrom.

A single anchor leg mooring system as illustrated, for instance, inFlory et al. US. Pat. No. 3,641,602 provides for mooring of very largevessels such as super tankers in the open sea and for transfer of cargo,as petroleum, to and from the vessel through a floating hose or hosesand vertical pipes and/or hoses extending to a pipeline on the seabed.As the buoy and the upstanding pipe shaft oscillate and tilt due to waveand wind action, the pivotally attached hose arm, which is aupported bya buoyancy tank at its outer end, tends to correspondingly rock and maystrike the buoy or cause excessive strains in the attached hose. Withoutthe stabilizing arrangement described herein, the hose arm has novertical stability at all, except for the relatively ineffectiverestraint provided by the stiffness of the attached hose leading to thewater surface. This hose is usually extremely flexible and the properalignment at the arm and hose often cannot be maintained satisfactorilyeven under calm weather conditions. This lack of stability causes thehose arm to droop too far down or to rise too high for satisfactoryfunction of the hose arm.

Consequently, the main object of the present invention is to providemeans for avoiding excessive swivelling and oscillation of the hose armin a single anchor leg mooring system and to maintain the armsubstantially in its optimum position.

SUMMARY OF THE INVENTION In accordance with the invention, the hose arm,which is pivotally connected to the upstanding pipe extending betweenthe mooring buoy chain and the seabed anchor and extends laterallytherefrom, is provided with distal buoyancy tank means for supportingthe arm and hose connected thereto. In addition, a ballast weight iscarried by the arm near its outer extremity and substantially beneaththe longitudinal center line of the arm so that as the arm pivots in avertical plane, the tendency of the weight to remain stably positionedvertically beneath the buoyancy tank tends to counteract the forcestending to produce such arm pivoting.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings whichillustrate the invention,

FIG. 1 is a perspective view of a single anchor leg mooring and cargotransfer device.

FIG. 2 is a schematic top view showing the hose arm portion of thedevice.

FIG. 3 is a side view of the structure in FIG. 2.

FIGS. 4, 5, and 6 are schematic views showing the hose arm in itsoptimum position and swivelled to various positions vertically andillustrating the compensating effect of the invention.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT OF THE INVENTION FIG. 1illustrates a single anchor leg mooring apparatus including a baseportion 8 firmly anchored 'to the seabed and into which the seabedpipeline 9 extends. Pipeline 9 communicates with an upstanding pipeshaft 10 connected to the base by a universal joint 11 and extends to abuoy chain 12 which at its upper end is attached to a buoy 13 having abracket 14 to which the vessel mooring line 15 may be attached. At thetop of the pipe shaft 10 there is provided a horizontally rotablecoupling 16 having horizontally opposed swivel joints 17 and 18 fromwhich project the yoke 19 form ing the laterally projecting hose arm towhich is connected the hose 20 leading to the tanker or other vessel tobe serviced. This mooring and cargo transfer arrangement, as more fullydescribed and claimed in Flory et al. US. Pat. No. 3,641,602, enablesthe vessel secured by mooring line 15 to rotate about the mooringapparatus under the influence of wind and waves with minimum mooringline forces and without the danger of fouling or damaging the hose 20,or other components of the mooring facility.

A buoyancy tank 24 is mounted on hose arm 19 near the outer extremitythereof. However, in case of severe rocking or tilting of pipe shaft 10or in case there is a change in the specific gravity of the cargo insidethe hose 20, the attitude of yoke-arm l9 and the hose 20 may be alteredsuch that the hose may drop or rise excessively, possibly causing thearm to strike the buoy or pipe 10 or otherwise endanger hose 20 or thehose arm. In order to avoid such dangerous conditions, the ballastweight 25 is rigidly supported beneath the center line of arm 19 and ata substantial distance outwardly from pipe 10. While ballast weight 25is shown supported substantially vertically beneath the buoyancy tank24, this arrangement is not essential. Rather the weight should bepositioned so that in its normal stable position the arm will be in itsoptimum position relative to pipe 10 and its connected hose 20.Preferably, the

Operation As arm 19 tends to pivot above (FIG. 5) or below (FIG. 6) itsoptimum position (FIG. 4), the effective moment arm of ballast weight 25will be, respectively, increased or decreased by the value a sin a(FIGS. 5 and 6). This results in a restoring or stabilizing forcesubstantially equal to Q a sin a where Q is the submerged weight ofballast 25, a is the distance between the center of the buoyancy forceand the ballast weight 25 (FIG. 4), and a sin a is the moment armincrement upon tilting of the hose arm. The relationship of buoyancytank 24 and ballast 25 may be varied, particularly in order to vary theoptimum positioning of the hose arm from that shown in FIG. 4.

The particular form of mooring apparatus is not essential and others maybe substituted; for instance, the swivelling hose and anchor lineconnections may be provided in the base of the apparatus. The inventionmay be modified in various respects as will occur to those skilled inthe art, and the exclusive use ofall modifications as come within thescope of the appended claims is contemplated.

I claim:

1. In a single point mooring system of the type having a buoy with meansfor mooring of a vessel thereto, a base anchored to the sea bottom, anupstanding cargo pipe shaft pivotally connected to said base andextending upwardly therefrom, a hose arm projecting laterally from theupper portion of said pipe shaft, a hose extending from said arm forcarrying cargo to and from a vessel moored to said buoy, buoyancy tankmeans for supporting said arm in substantial alignment with said hose,and a pivotal connection between said arm and said pipe shaft permittingvertical swivelling of said arm relative to said pipe shaft, and hosearm stabilizing means comprising a ballast weight carried by said armsubstantially laterally outwardly of said pipe shaft and substantiallybeneath the center of buoyancy of said arm and buoyancy tank meansthereby causing a stabilizing effect which counteracts external forcestending to dislodge the arm from its proper position.

2. In a single point mooring system of the type having a buoy with meansfor mooring of a vessel thereto, a base anchored to the sea bottom, astructure pivotally connected to said base and extending upwardlytherefrom, a hose arm projecting laterally from said structure, a hoseextending from said arm for carrying cargo to and from a vessel mooredto said buoy, buoyancy tank means for supporting said arm in substantialalignment with said hose, a pivotal connection between said arm and saidpipe shaft permitting vertical swivelling of said arm relative to saidpipe shaft, and hose arm stabilizing means comprising a ballast weightcarried by said arm substantially laterally outwardly of said pipe shaftand substantially beneath the center of buoyancy of said arm andbuoyancy tank means thereby causing a stabilizing effect whichcounteracts external forces tending to dislodge the arm from its properposition.

1. In a single point mooring system of the type having a buoy with meansfor mooring of a vessel thereto, a base anchored to the sea bottom, anupstanding cargo pipe shaft pivotally connected to said base andextending upwardly therefrom, a hose arm projecting laterally from theupper portion of said pipe shaft, a hose extending from said arm forcarrying cargo to and from a vessel moored to said buoy, buoyancy tankmeans for supporting said arm in substantial alignment with said hose,and a pivotal connection between said arm and said pipe sHaft permittingvertical swivelling of said arm relative to said pipe shaft, and hosearm stabilizing means comprising a ballast weight carried by said armsubstantially laterally outwardly of said pipe shaft and substantiallybeneath the center of buoyancy of said arm and buoyancy tank meansthereby causing a stabilizing effect which counteracts external forcestending to dislodge the arm from its proper position.
 2. In a singlepoint mooring system of the type having a buoy with means for mooring ofa vessel thereto, a base anchored to the sea bottom, a structurepivotally connected to said base and extending upwardly therefrom, ahose arm projecting laterally from said structure, a hose extending fromsaid arm for carrying cargo to and from a vessel moored to said buoy,buoyancy tank means for supporting said arm in substantial alignmentwith said hose, a pivotal connection between said arm and said pipeshaft permitting vertical swivelling of said arm relative to said pipeshaft, and hose arm stabilizing means comprising a ballast weightcarried by said arm substantially laterally outwardly of said pipe shaftand substantially beneath the center of buoyancy of said arm andbuoyancy tank means thereby causing a stabilizing effect whichcounteracts external forces tending to dislodge the arm from its properposition.